[Samba] slow speeds with Windows 10

[Xen]

I was transferring a file from a (slow) smbd server running on some NAS.

The transfer speed is only 1MB/s but the NAS uses 100% CPU. Normally the 
NAS can handle 60MB/s download (from the NAS).

Could it be that the connection uses encryption or something?

What could be causing this slow speed?

I have internet download speeds over this same connection surpassing 
5MB/s. I cannot imagine why something like this would be so slow.